JPH059522B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a split yarn made of vinylidene fluoride resin, a method for producing the same, and a filter using the split yarn.

BACKGROUND TECHNOLOGY Yarns made from continuous fibers in vinylidene fluoride resins, that is, filament yarns, have been industrialized, but yarns made from staple fibers, that is, split yarns, have not yet been industrially obtained. .

Split threads are difficult to obtain with many resins, not just vinylidene fluoride resins. Split yarns known up to now include polypropylene yarns, which are obtained by cold-stretching polypropylene at a high draw ratio of around 10 times and then splitting it. Split yarns have not been obtained from the resin. The reason is that polypropylene has a high degree of crystallinity,
It is thought that this is because the intermolecular cohesive force is weak, making it easy to split, making it easy to apply the above method.

Therefore, it was thought that it would be difficult to obtain split yarns using the splitting method described above for vinylidene fluoride resins, which have a lower degree of crystallinity and greater intermolecular cohesive force than polypropylene. It is.

However, vinylidene fluoride resin is a polar polymer and has inherently superior properties such as weather resistance and chemical resistance compared to polypropylene, so its charged split yarn If obtained, it is expected that it will become a functional material useful as, for example, a filter.

OBJECTS OF THE INVENTION In view of the current situation, the main object of the present invention is to provide a charged split yarn made of vinylidene fluoride resin, a method for producing the same, and a filter using the split yarn.

Summary of the Invention According to research conducted by the present inventors, it has been found that a charged vinylidene fluoride resin split yarn can be obtained by treating a vinylidene fluoride resin having an appropriate molecular weight under appropriate conditions, and that It has been found that the vinylidene fluoride resin split yarn obtained by this method has a characteristic crystal melting point and crystal size, and because of its stable surface charge, it has excellent dust removal properties and can be used as a useful filter material.

The vinylidene fluoride resin split yarn of the present invention is based on such knowledge, and more specifically, it is characterized by satisfying the following requirements (a) to (c).

(a) It has a crystal melting point of approximately 182°C or higher when heated in a nitrogen atmosphere at a heating rate of 10°C/min using a differential scanning calorimeter; (b) The average crystal width size is approximately 200 Å or more. and (c) have a surface charge.

Further, the method for producing vinylidene fluoride resin split yarn of the present invention is characterized by including the following steps (a) to (e).

(b) Use dimethylacetamide as the solvent and adjust the concentration to
Inherent viscocity is 0.8 to 1.4 dl/g under conditions of 0.4 g/dl and concentration at 30°C.
A step of melt-extruding a vinylidene fluoride resin into a sheet or tube shape, (b) cooling and solidifying it while draft stretching in the melt-extruded state to form a film having a birefringence of 25×10 ^-3 or more; (c) heat-treating the film at a temperature of 80 to 180°C; (d) forming a vinylidene fluoride resin at any point between after step (b) and after step (c). a step of applying a voltage to the film at a temperature higher than the glass transition temperature and lower than the melting point of the main resin; and (e) a step of splitting the film.

Further, the filter of the present invention is characterized in that it is composed of an aggregate of the above-mentioned vinylidene fluoride resin split threads.

The present invention will be explained in more detail below.

Detailed Description of the Invention In the present invention, "vinylidene fluoride resin" refers to a vinylidene fluoride homopolymer, 70 mol% or more of vinylidene fluoride as a structural unit, and one monomer copolymerizable with the vinylidene fluoride homopolymer. The term "vinylidene fluoride resin composition" includes a species or a copolymer consisting of two or more species, and a vinylidene fluoride resin composition containing at least 80% by weight of at least one of these species.

Components other than the vinylidene fluoride alone or copolymer constituting the composition include other polymers, plasticizers, processing aids, and additives such as ultraviolet absorbers. Examples of other polymers include polymers, etc. Inside are polyethylene, polypropylene, polyvinyl acetate,
Examples include polymethyl methacrylate, polyethyl methacrylate, polystyrene, fatty acid polyester, aromatic polyester, polyamide, and fluorine-based polymers excluding vinylidene fluoride.

In the present invention, among the vinylidene fluoride resins mentioned above, vinylidene fluoride homopolymer or vinylidene fluoride is used as a constituent unit in an amount of 70 mol%.
In particular, a copolymer of vinylidene fluoride and perfluoroolefin containing 80 mol% or more, particularly a copolymer of vinylidene fluoride and ethylene tetrafluoride, is preferably used.

The vinylidene fluoride resin split yarn of the present invention is mainly determined by its post-drafting state during its manufacturing process, but is exposed to nitrogen at a heating rate of 10°C/min using a differential scanning calorimeter (DSC). It has a melting point of about 182°C or higher when heated in an atmosphere. Here, the crystal melting point refers to the endothermic peak of DSC.

Among them, resins with a larger proportion of the endothermic area based on the melting endothermic peak of 182°C or higher in the endothermic area of DSC are more likely to form split yarns. For example, when splitting a film to make a split yarn, the yarn tends to split easily and has a large Young's modulus. Therefore, in the endothermic area of DSC,
The ratio of the endothermic area based on the melting endothermic peak of about 182° C. or higher is preferably 20% or more, more preferably 50% or more, even more preferably 80% or more.

Also, for the same reason, it is preferable to have a crystal melting point at a higher temperature, preferably 185°C or higher, and even more preferably 190°C or higher. Moreover, it is preferable that the proportion of the endothermic area based on the melting endothermic peak at the temperature above the above-mentioned temperature increases in the endothermic area of the DSC measurement chart, and it is even more preferable that the proportion is the same as that described above for temperatures above 182°C. .

The baseline for determining the endothermic area of the DSC measurement chart explained above is determined as follows.

First, measure the measurement sample under the measurement conditions already described.
Raise the temperature to 220℃ and obtain the melting curve of the crystal. At this time, the temperature was continuously maintained at 220°C for 30 seconds, and then the temperature was lowered at a rate of 10°C/min to crystallize and cool to room temperature. The melted recrystallized product thus obtained is heated again under the same conditions to obtain a crystal melting curve. The first crystal melting end point of the obtained crystal melting curve, that is, the point at which the exothermic peak ends (Tmid) is determined (see FIG. 1, which was determined for Examples described later).

Locate the melting peak of the melting curve of the measurement sample at this point.
Tmid, while there is no heat balance at the highest and lowest temperature sides of the melting curve (Tmax and
Tmin) are connected to the point Tmid to form the baseline.

Note that both ends with no heat balance are obtained with no sample included, assuming all other conditions are the same.
Its position is determined by superimposing the DSC measurement charts.

In addition, the split yarn of the present invention is made of crystals with an average crystal width size of approximately 200 Å or more, and is usually 250 Å or more.
It is about ~350 Å. Here, the average crystal width size is determined by X-ray diffraction. That is, the sample is a collection of split yarns aligned approximately in the draft direction and hardened into a film with an amorphous adhesive. With the draft direction of this sample in the vertical direction,
The X-ray reflection intensity in the horizontal direction on the film surface, that is, the diffraction intensity is recorded on a chart. In determining the average crystal width size from the obtained chart, we focus on the diffraction peak of the (110) plane. That is, the diffraction intensity of the (110) plane is read on a chart, and the half width of the peak is determined. On the other hand, using a silicone single crystal powder, the mechanical spread (that is, the spread of the diffraction peak specific to the measuring machine) under the measurement conditions is determined. The value obtained by subtracting the half-width value of mechanical expansion from the half-width value of the measurement sample is defined as the true half-width value (βw (radians)) of the sample. Using this true half-width value, the crystal width (L) is determined from Schierer's equation L=k·λ/βw·cosθ.

where θ is the measured diffraction surface (i.e. (110)
The Bragg reflection angle of the surface), k is a constant (=1.0), and λ is the wavelength of Cukα of the X-ray (1.542 Å).
(For details on such measurement methods, see, for example, p. 569 of "Fundamentals of X-ray Crystallography", co-translated by Hirabayashi and Iwasaki, Maruzen (published August 30, 1972)). The measured values in this specification were taken using an X-ray diffractometer manufactured by Rigaku Corporation, and the voltage-current was 40KV-20mA. The condition is 1°, and the scanning speed is 2θ of 1°/
It was determined under the conditions of . Also, X-rays
It was made monochromatic with a Ni filter.

Furthermore, the split yarn of the present invention can be obtained as a split yarn having a higher Young's modulus than generally known polypropylene split yarns. This is surprising compared to the fact that the Young's modulus of polyvinylidene fluoride filaments known up to now is smaller than that of polypropylene filaments. Although it is common to conventional vinylidene fluoride resins, the split yarn of the present invention has excellent weather resistance and chemical resistance, which is an excellent feature that polypropylene split yarn does not have.

The split yarn of the present invention has a surface charge. Here, the phrase "having a surface charge in a split yarn" does not simply mean that the yarn has a surface charge temporarily, but rather that it has a surface charge semi-permanently. Specifically, the presence or absence of surface charge was determined by using split yarn in the form of woven or non-woven fabric (size: 10 cm x 10 cm).
cm) and kept at 23℃ and 50% humidity for 24 hours.
Under these conditions, it can be identified by whether the arithmetic average value of the five surface potentials measured with a rotating sector type surface potential meter maintains 1V or more.

Split yarn made of vinylidene fluoride resin with such a surface charge has a superior dust removal effect based on its surface charge compared to polypropylene split yarn which has a surface charge, and is particularly effective at filtering out dust in the air, cigarette smoke, etc. Suitably used. However, the filter is not limited to the air filter described above. That is, the object to be treated is not limited to air, but can be preferably applied to all fluids that exhibit a gaseous or mist-like state during treatment, especially gases, or non-polar liquids.

The surface-charged vinylidene fluoride resin split yarn of the present invention can be obtained, for example, by the following method.

That is, first, the coherent viscocity of a solution in dimethylacetamide with a concentration of 0.4 g/dl at a concentration of 30°C is 0.85 to 1.4 dl/dl.
The vinylidene fluoride resin (g) is melt-extruded into a sheet or tube shape. If the inherent viscocity is smaller than this range, unevenness in thickness is likely to occur during drafting, which will be described later, making it difficult to obtain a substantially high draft rate, leading to a decrease in mechanical strength.
Furthermore, if the inherent viscocity is larger than this range, molding becomes difficult and thermal decomposition tends to occur when molded at high temperatures. Preferably, the inherent viscocity based on the above criteria is 0.9 to 1.3.
dl/g, more preferably 1.0 to 1.2 dl/g.

As the extrusion method, known methods such as T-die method and inflation are employed. Preferably, a method is employed in which the film is produced by extrusion using a circular inflation die and then by an inflation method. The reason for this is that the width shrinkage is large in the T-die method, so that if a high draft is subsequently applied, both ends of the film will be insufficiently oriented, which is undesirable.

After melt extrusion, the product is cooled and solidified into a film while being draft stretched at a high draft rate.
The draft rate at this time is selected so that the birefringence of the film after cooling and solidification is 25×10 ⁻³ or more.

To explain this point in a little more detail, after melt-extruding the vinylidene fluoride resin, the temperature indicating the maximum crystallization rate of the main resin constituting the vinylidene fluoride resin (hereinafter abbreviated as "maximum crystallization rate temperature") or lower When winding a film at an ambient temperature of 100 mL and a pinch roll temperature below the maximum crystallization rate temperature, a film with oriented polymers can be obtained if the film is wound at a high draft rate higher than a certain draft rate. At this time, the draft rate varies depending on the melt viscosity of the resin, ambient temperature, cooling air volume, etc., but it is wound at a high draft rate so that the birefringence Δn of the obtained film is about 25 × 10 ^-3 or more. The film thus obtained has crystals with a high melting point of 182° C. or higher, unlike films with a birefringence lower than that, and its Young's modulus increases rapidly, as shown in FIG. 2. (Figure 2 shows vinylidene fluoride homopolymer with an inherent viscocity of 1.1 dl/g, a die temperature of 240°C, and a die diameter of 50°C.
This graph shows the relationship between Δn and Young's modulus of films extruded from a circular die with mmφ and lip clearance of 2 mm and wound at various winding speeds at a blow-up ratio of 1.2. In this way, it has high melting point crystals,
Winding at a draft rate higher than the draft rate at which the Young's modulus begins to increase rapidly is referred to herein as draft stretching.

An appropriate draft rate depends on the melt viscosity of the resin, but is usually about 50 to 5,000. When the melt viscosity of the resin is low, the draft ratio must be set to a relatively large value in order to achieve a birefringence of 25×10 ⁻³ or higher after cooling and solidification. Preferably, the birefringence is 30×10 ^-3 or more, more preferably 35
Choose a draft rate so that it is at least ×10 ^-3 . This is because the splitting process described later becomes easier.

In the case of the inflation method, the draft ratio and the blow-up ratio, which is the stretching ratio in the width direction, are selected as appropriate, and are usually in the range of 0.7 to 2.5, preferably in the range of 0.8 to 1.5.

A known method is used for cooling and solidifying, but
For example, in the case of an inflation method, the material may be extruded upward, cooled with air, and then wound up, or extruded downward, and typically cooled with a coolant such as water.

The film thus obtained was heated to 80 to 180℃.
heat treated at a temperature of

This heat treatment is carried out to promote crystallization, and it is efficient to carry out the heat treatment at around the maximum crystallization rate temperature of the main resin constituting the vinylidene fluoride resin. Therefore, preferably the temperature does not fall below 60°C below the maximum crystallization rate temperature and does not exceed 60°C above the maximum crystallization rate temperature, even more preferably does not fall below 40°C below the maximum crystallization rate temperature and the maximum crystallization rate temperature This is done at a temperature not exceeding 40°C above the speed temperature.

The longer the heat treatment time, the better, but it is usually carried out at the maximum crystallization rate temperature for at least 2 hours,
More preferably, it is carried out for 24 hours or more.

Although it is not necessary to keep the film in a constant length state during heat treatment like a cold stretched film, it is desirable that the film be in a constant length state. By such heat treatment, the crystal structure of the vinylidene fluoride resin constituting the film is transformed from a structure mainly consisting of an α-type structure to a structure mainly consisting of a γ-type structure.

It is preferable that the film is cold-stretched after or together with the heat treatment to transform the crystal structure into one mainly having a β-type structure. This is because the film has higher elasticity and is more likely to become split yarn.

The stretching ratio at this time is about 1.1 to 5.0 times.

At any stage after the draft stretching cooling solidification step and after the heat treatment step, that is, before the heat treatment step, simultaneously with the heat treatment step, during the heat treatment step, or after the glass transition of the main resin constituting the vinylidene fluoride resin. A voltage is applied to the film at a temperature higher than the temperature and lower than the melting point. A voltage is usually applied in the thickness direction of the film at a magnitude of 50 KV/cm or more and less than the dielectric breakdown strength. The purpose of applying such a voltage is to impart a surface charge to the resulting split yarn. Therefore, the voltage may be applied while the crystallization progresses in the film, or the voltage may be applied after the crystallization is almost completed, but the latter is more efficient.
That is, it is preferable to carry out the process after the heat treatment process or in the middle of the heat treatment process. However, after becoming a split yarn,
Applying a voltage is not suitable for effective charge application because the withstand voltage of the air existing in the gaps between the threads is low and high voltage cannot be applied.

The temperature at which the voltage is applied can be within a range with the lower limit being the glass transition temperature of the main resin constituting the vinylidene fluoride resin and the upper limit being less than the melting point, but is preferably in the range from room temperature to 150°C, more preferably room temperature. to 120℃. The voltage may be applied either with the electrodes in close contact with both the films or with the electrodes slightly separated from each other, that is, with corona treatment.
Corona treatment is preferable when a voltage is continuously applied to the film. In either method, an application time of several seconds to several tens of minutes is usually sufficient. Although the application time may be long, it reduces productivity, so the above range is preferably used.

The film thus obtained is split and has an average diameter of, for example, 1 to 10 μm on the short side and 2 to 10 μm on the long side.
Split yarn with a rectangular cross section of 100 μm.

The film is split by using, for example, a needle roll as disclosed in JP-A-58-180621 and rotating the roll in contact with the film along the transport direction.

The filter of the present invention can be obtained by forming the obtained split yarn into a cloth-like body such as a woven or non-woven fabric suitable for cleaning a fluid, or an aggregate such as a filler to be filled in a flow path.

Effects of the Invention As explained in detail above, according to the present invention, by treating vinylidene fluoride resin having an appropriate molecular weight through a specific process bond, vinylidene fluoride resin Resin split yarns are obtained, and the surface-charged split yarns have better chemical resistance such as weather resistance and chemical resistance compared to polypropylene split yarns, which are almost the only synthetic resin split yarns that have been previously obtained. Not only does it have excellent mechanical properties, but it also becomes a split yarn with a higher Young's modulus. Furthermore, since the vinylidene fluoride resin itself is a polar polymer, the surface charge is maintained extremely stably on the split yarn, forming a filter that is highly effective in removing minute charged particles from various fluids including air. Ru.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Vinylidene fluoride homopolymer with an inherent viscocity of 1.15 dl/g (measured at 30°C and a concentration of 0.4 g/dl using dimethylformamide as a solvent) obtained by suspension polymerization at 25°C. was extruded upward using an extruder having a circular die with a diameter of 50 mm and a lip clearance of 3.0 mm at an extrusion temperature of 240°C and an extrusion rate of 60 g/min.

Inflation was performed at a blow-up ratio of 1.5 and a winding speed of 50 m/min while cooling with air at an air flow rate of 0.01 m ³ /min from an air ring installed approximately 10 cm above the die. Therefore, the draft rate (R ₁ )
is 670, and the birefringence of the obtained film is 36
It was ×10 ^-3 .

In this way, the blown film was wound up into a paper tube and kept at 90°C for 20 minutes.
Heat treated in a gear oven for 1 day.

Furthermore, the average width size of the crystals determined from X-ray diffraction was 320 Å. Furthermore, in a nitrogen atmosphere using DSC
When observing the melting behavior of the crystal at a heating rate of 10℃/min,
As shown in FIG. 1, the crystallization point showed double peaks at 175°C and 195°C, and the ratio of the endothermic area based on the melting endothermic peak at 195°C was about 50%.

This film was further stretched 1.3 times at 150°C.

This film was subjected to corona polarization using a corona polarization device having needle-shaped electrodes on both the upper and lower surfaces, with a distance between the needle tip and the film of approximately 5 mm, and a voltage of 1.5 KV applied at a film running speed of 0.5 m/min. .

As a result of splitting this stretched and corona-treated film using a needle type splitting device, it has a fine rectangular cross section with an average short side of 3 μm and an average long side of 15 μm.
A slit thread with an average length of 20 cm was obtained.

Example 2 A nonwoven fabric of 0.05 g/cm ² was formed using the split yarn obtained by the method of Example 1, and had a diameter of 30 mm and a length of 20 mm.
This membrane was placed in the middle of a cm glass tube, and a commercially available household whirlpool blower was placed 30 cm away from one side to send cigarette smoke along with the wind. Almost no cigarette smoke was observed in the glass tube on the other side of the membrane.

Comparative Example Example 2 except that a filter having a rectangular cross section with an average short side of 3 μm and an average long side of 15 μm, and a non-woven fabric of 0.05 g/cm ² of isotactic propylene split yarn with an average length of 20 cm was used. When the same procedure as above was carried out, the cigarette smoke was only slightly diluted, and a clear difference was observed compared to the case where the vinylidene fluoride resin split yarn of the present invention was used.

[Brief explanation of the drawing]

FIG. 1 is an example of a melting curve measured with a differential scanning calorimeter, and FIG. 2 is a graph showing the relationship between Young's modulus and birefringence, etc. to explain draft stretching.

Claims (1)

[Scope of Claims] 1. A vinylidene fluoride resin split yarn characterized by satisfying the following requirements (a) to (c). (a) It has a crystal melting point of approximately 182°C or higher when heated in a nitrogen atmosphere at a heating rate of 10°C/min using a differential scanning calorimeter; (b) The average crystal width size is approximately 200 Å or more. and (c) have a surface charge. 2. A method for producing vinylidene fluoride resin split yarn, which includes the following steps (a) to (e). (b) Use dimethylacetamide as the solvent and adjust the concentration to
Inherent viscocity is 0.8 to 1.4 dl/g at a temperature of 0.4 g/dl and a temperature of 30°C.
A step of melt-extruding a vinylidene fluoride resin into a sheet or tube shape, (b) cooling and solidifying it while draft stretching in the melt-extruded state to form a film having a birefringence of 25×10 ^-3 or more; (c) heat-treating the film at a temperature of 80 to 180°C; (d) forming a vinylidene fluoride resin at any point between after step (b) and after step (c). a step of applying a voltage to the film at a temperature higher than the glass transition temperature and lower than the melting point of the main resin; and (e) a step of splitting the film. 3. A filter comprising an aggregate of vinylidene fluoride resin split yarns that satisfies the following requirements (a) to (c). (a) It has a crystal melting point of approximately 182°C or higher when heated in a nitrogen atmosphere at a heating rate of 10°C/min using a differential scanning calorimeter; (b) The average crystal width size is approximately 200 Å or more. It must consist of a certain crystal, and (iii) it must have a surface charge.